Any slipping or erratic shifting and even being only 1L down can easily damage the transmission much less 2 or 3 Liters.
They’ve botched this not once, but twice, so now the aggravation will begin. If your transmission goes completely belly-up in 6 months, a year, or whatever this incident will be the cause of it and you can fully expect in the above mentioned time frames the excuses will begin about why if they were at fault it would have died from the start, yada, yada, yada.